The present invention relates to compositions for optical fiber coatings and fiber optic ribbon matrixes, optical fibers that contain a secondary coating prepared from such compositions, methods of making such optical fibers, and fiber optic ribbons that contain a matrix prepared from such compositions.
Optical fibers have acquired an increasingly important role in the field of communications, frequently replacing existing copper wires. This trend has had a significant impact in the local area networks (i.e., for fiber-to-home uses), which has seen a vast increase in the usage of optical fibers. Further increases in the use of optical fibers in local loop telephone and cable TV service are expected, as local fiber networks are established to deliver ever greater volumes of information in the form of data, audio, and video signals to residential and commercial users. In addition, use of optical fibers in home and commercial business environments for internal data, voice, and video communications has begun and is expected to increase.
Optical fibers typically contain a glass core and at least two coatings, e.g., a primary (or inner) coating and a secondary (or outer) coating. The primary coating is applied directly to the glass fiber and, when cured, forms a soft, elastic, and compliant material which encapsulates the glass fiber. The primary coating serves as a buffer to cushion and protect the glass fiber core when the fiber is bent, cabled, or spooled. The secondary coating is applied over the primary coating and functions as a tough, protective outer layer that prevents damage to the glass fiber during processing and use.
Certain characteristics are desirable for the secondary coating. Before curing, the secondary coating composition should have a suitable viscosity and be capable of curing quickly to enable processing of the optical fiber. After curing, the secondary coating should have the following characteristics: sufficient stiffness to protect the encapsulated glass fiber yet enough flexibility for handling (i.e., modulus), low water absorption, low tackiness to enable handling of the optical fiber, chemical resistance, and sufficient adhesion to the primary coating.
To achieve the desired characteristics, conventional secondary coating compositions generally contain urethane-based oligomers in large concentration, with monomers being introduced into the secondary coating composition as reactive diluents to lower the viscosity. Because conventional oligomeric components are, in general, much more expensive than the monomeric components, the use of oligomers in high concentration has the effect of increasing the cost of producing secondary coating compositions as well as the resulting optical fiber. Despite the cost of using oligomeric components in high concentration, it is believed that there are no commercially viable secondary coating compositions that either contain a low concentration or are completely devoid of oligomeric components.
Thus, there remains a need for suitable secondary coating compositions which can be prepared at lower cost than conventional secondary coating compositions and yield secondary coatings with a suitable modulus and other physical properties. The present invention is directed to overcoming this deficiency in the art.
There is also a need for a coating that will reduce the sensitivity of the fiber to bending, particularly microbending. This is especially relevant for high data rate optical fiber. A high data rate fiber is typically a single mode fiber with a large effective area. Fibers with a large effective area have an increased signal mode transmission capacity in comparison to non-large effective area fibers. However, fibers with a large effective area have a greater sensitivity to stresses, such as stresses caused by bending the fiber. These stresses can lead to distortion of the optically active region of the fiber and result in microbend signal attenuation.
The present invention relates to a composition for coating optical fibers and optical fiber coated with the composition. One aspect of the invention comprises an optical fiber coating composition. The coating composition comprises an UV curable composition and when cured exhibits a Young""s modulus of about 950 MPa or more and a film to film coefficient of friction of less than about 0.44. A second aspect of the invention comprises an optical fiber having a core and a cladding coated with the aforementioned coating.
A third aspect of the invention comprises a coated optical fiber comprising an optical fiber having a core and a cladding, and a coating composition and when cured the coating exhibits a Young""s modulus of at least about 950 MPa or more and a fiber to fiber coefficient of friction of no more than about 0.74. Preferably the fiber to fiber coefficient of friction is measured at a speed of about 0.423 cm/sec and with a weight of about 100 grams.
The composition of the present invention has suitable characteristics which enable its use in preparing the outer coating material on optical fibers and the matrix material on fiber optic ribbons. Moreover, when cured, the composition results in a coating or matrix material that possesses desirable characteristics with respect to water absorption, reduced microbend sensitivity, and extraction, as well as strength or modulus. Thus, suitable coating or matrix materials can be prepared from a composition that contains little or no oligomeric components, which significantly reduces the cost of preparing such compositions as well as the optical fibers and fiber optic ribbons that contain the cured product of such compositions.
An optical fiber coated with the inventive UV curable composition has the advantage of exhibiting reduced xe2x80x9cslip-stickxe2x80x9d behavior to desirable levels, preferably eliminating slip-stick, without compromising the mechanical properties of the coated fiber. xe2x80x9cSlip-stickxe2x80x9d behavior includes at least when a fiber is either being wound onto a spool or paid off of a spool and the coated fiber repeatedly sticks to the adjacent fiber below the fiber and then slips over the adjacent fiber below and then sticks again. xe2x80x9cSlip-stickxe2x80x9d behavior is further described below with respect to FIG. 3.
A fiber coated with the inventive UV curable coating composition has also exhibited desirable optical time domain reflectometry (xe2x80x9cOTDRxe2x80x9d) results. The favorable OTDR results include desirable wind-induced attenuation results. Favorable wind-induced attenuation results correlate to a fiber with improved handability in the rewinding, ribboning, and cabling processes.
Another advantage of the inventive composition is that the composition minimizes, preferably eliminates, the xe2x80x9cblooming effectxe2x80x9d of uncured coating components, such as a monomer, or unreacted coating components. An example of the blooming effect is when a monomer or other coating component migrates to the coating surface. One reason for blooming effect is the migration of non-fully cured components which migrate or result on the surface of the optical fiber coating.
Preferably the inventive coating protects the fiber from handling and environmental abuse. Preferably, the inventive minimizes wind-induced attenuation.